An alkaline rechargeable battery is a battery repeatedly chargeable-dischargeable and has been widely used as a power source for portable devices. In particular, a nickel metal hydride rechargeable battery, which employs a hydrogen-absorption alloy as a negative electrode active material, has high energy density and is relatively environmentally clean. A nickel metal hydride rechargeable battery is therefore becoming widespread as a main power source of various portable devices.
In a current collecting method in a nickel metal hydride rechargeable battery, a closed-end tubular container which contains an electrode assembly including positive and negative electrodes serves as a negative electrode terminal, and a sealing plate insulated from the container serves as a positive electrode terminal. The positive electrode is integrated with the sealing plate through a lead to form a current collecting structure, whereas the outermost peripheral portion of the negative electrode contacts an inner side wall of the closed-end tubular container to form a current collecting structure.
In a nickel metal hydride rechargeable battery, oxygen gas generated at the positive electrode during overcharging reacts with hydrogen stored in a hydrogen-absorption alloy serving as a negative electrode active material to reduce the oxygen to water, thereby providing a reaction mechanism for spontaneously suppressing an increase of the pressure inside the battery. In order to facilitate this reaction, a method has been proposed in which a graphite intercalation compound capable of absorbing and emitting hydrogen is provided on the surface of the negative electrode to facilitate movement of oxygen gas generated at the positive electrode to the negative electrode (see, for example, Patent Document 1).    [Patent Document 1] Japanese Patent Laid-Open Publication No. Hei 5-335015.